1. Field of the Invention
The present invention relates to a power clamping circuit with temperature compensation, and more particularly, to a power clamping circuit capable of generating a system voltage with a substantially zero temperature coefficient via adjusting a resistance ratio.
2. Description of the Prior Art
A traditional power clamping circuit may be a single Zener diode, or composed of several cascaded transistors. Please refer to FIG. 1A and FIG. 1B, which are schematic diagrams of two types of power clamping circuits 10 and 15. As shown in FIG. 1A, a cathode of a Zener diode VZ is coupled to a system voltage VBAT, and an anode of the Zener diode VZ is coupled to a ground to form a reverse bias on the Zener diode VZ. As well known in the art, when the reverse bias, i.e. the system voltage VBAT, is greater than a breakdown voltage of the Zener diode VZ, a breakdown current is generated on the Zener diode, and the breakdown current flows to the ground to decrease the reverse bias to be lower than the breakdown voltage. As a result, as long as the breakdown voltage of the Zener diode VZ is properly chosen, the system voltage VBAT may be limited to be lower than the breakdown voltage to achieve power clamping.
Similarly, as shown in FIG. 1B, the power clamping circuit 15 is composed of transistors M1-MM, when the system voltage VBAT is greater than a sum of threshold voltages V1-VM of the transistors M1-MM, the transistors M1-MM are turned on to decrease the system voltage VBAT to be lower than the sum of the threshold voltages V1-VM to achieve power clamping.
However, the above traditional power clamping circuits are both susceptive to temperature. Thus, the breakdown voltage of the Zener diode varies with the temperature. Moreover, the threshold voltages V1-VM of the transistor M1-MM increase as the temperature decreases, i.e. a negative temperature coefficient. When the temperature is high, the transistors M1-MM are easily turned on to perform the power clamping to the system voltage VBAT. In other words, the system voltage VBAT may be much lower when the temperature is high, which may reduce an operating efficiency of a system load. Therefore, there is a need to improve the prior art to mitigate temperature influence on the power clamping circuit.